In the past, the conventional means for storing perishable foods has involved the use of glass jars and metal cans which have an inherent oxygen barrier characteristic. In recent years, a new concept has emerged through the use of certain plastic materials which have low permeability to oxygen and moisture. One of the major methods of manufacture of plastic barrier containers involves the coextrusion of plastic sheet comprised of a barrier material and a less expensive matrix material. The sheet is heated and shaped by a thermoforming process.
The thermoforming process lends itself well to manufacture of plastic cans and a variety of tapered containers which can be sealed by a number of methods such as double seamed metal lids or adhesive sealed aluminum lids. One product for which thermoforming is not generally suitable is screw cap jars which represent a large portion of the food storage market. The thermoforming process does not normally provide sufficient wall thickness and rigidity at the open end necessary for a satisfactory screw type closure. The present invention provides a thermoformed screw top jar.